After electronic components have been mounted on printed wiring boards, a conformal coating is usually applied to the boards to protect the components from hostile environments such as high humidity and the presence of corrosive vapors. Conventional solvent-based conformal coating compositions produce coatings having good properties, but the compositions require a long time to dry (at least 5 minutes) and harmful solvents are evolved during the curing process. The best conformal coating today is considered to be "Parylene"; however, "Parylene" has to be processed by vacuum pyrolysis deposition, a very expensive and patented process.
Conformal coatings that are UV curable have the advantages that they can be cured rapidly (in seconds) with no volatile organic compounds being emitted, so they are well suited for an automated electronic assembly line. However, until now, an easily processed UV curable conformable coating composition which has the appropriate viscosity, has good tank life, and is capable of forming a coating having the required properties, has not been made.